Divertor Power Handling Assessment for Baseline Scenario Operation in JET in Preparation for the ILW
The ITER-Like Wall (ILW) project in JET is replacing the currently used Plasma Facing Components (PFCs), made with Carbon-Fibre Composite (CFC) by Be (wall) and W (divertor) for operation in 2011. This to mimic the proposed PFCs for the DT operational phase of ITER. The new W divertor is planned to have a central divertor target plate (tile 5 in figure 1(a)) made of solid W while the rest of the divertor target tiles are W coated CFC tiles. The bulk W row is segmented poloidally into 4 stacks per tile and toroidally in 24 lamellae per stack to minimise the eddy current loads. The tile segmentation and the support structure determines the power and energy limits on the divertor defining the tiles power and energy handling and therefore the level of additional heating and pulse length. Various techniques to reduce both continuous and transient power load on the divertor are being explored at JET, such as ELM mitigation by using resonant magnetic perturbation, vertical kicks to control the ELM frequency and nitrogen seeding to increase the plasma radiated power. The tile design gives rise to surface temperature limits (for the W coating) as well as bulk temperature limits (for the tile fixings). Recently, experiments have been carried out at JET to test the sweep amplitude necessary to reduce the power and energy loads to the divertor tiles while keeping the same H-mode performance as the reference non-swept plasma, for low and high triangularity configurations, similar to those carried out in 1991/1992.